1. Field of the Invention
This invention relates generally to apparatus which utilizes vessels, valves and connecting conduits for the intermixing and/or diluting of fluids primarily for the purpose of making measurements and tests upon said fluids. More particularly, this invention is concerned with the type of automatic analysis instrument such as disclosed in U.S. Pat. Nos. 3,549,994 and 3,567,390 which employ the Coulter particle analyzing principle disclosed in U.S. Pat. No. 2,656,508, and provides herein backwash means to assure sample integrity in the operation of such and like apparatus.
2. DESCRIPTION OF PRIOR ART
In recent years so-called automatic chemistry apparatus has become popular, especially where testing and measurements are to be performed on a continuous basis, with many tests to be made simultaneously and complex routines to be repeated, but with different samples. One such apparatus is disclosed in U.S. Pat. No. 3,549,994 and is primarily intended for the measurement of parameters of blood.
In that apparatus, samples of whole blood are introduced in succession, and the apparatus performs the requisite dilutions, tests and computations needed for obtaining such information as white and red cell count, hematocrit, hemoglobin measurement, etc. In the course of performing such determinations, necessary sample suspensions of predetermined concentration are prepared within the apparatus and transferred between vessels thereof. Multiple dilutions, mixing, pumping, transfer and moving of fluids between vessels are accomplished within the systems on an automatic or programmed basis and are effected by means of suitable valving apparatus as described in said U.S. Pat. No. 3,549,994 and particularly, an advantageous valving apparatus being that disclosed in U.S. Pat. No. 3,567,390.
In such systems, one can automatically produce one or more sample suspensions from a first fluid specimen, while simultaneously commencing dilution of the first of a second fluid specimen before the desired dilutions of the first are completed, the system employs a transfer valve structure wherein a fluid sample is drawn into a first portion of the valve. The valve then is indexed to subtend a precise amount of the sample and to mix same with a known quantity of diluent to provide a first fluid suspension of known concentration which is directed to a station. At the same time, the first diluted fluid suspension from the immediately preceding original sample, and at the said station, is drawn or "thiefed" into a second portion of the valve apparatus so that upon indexing of the valve back to its initial or start position, a precise amount of the last-mentioned suspension is subtended and mixed with a second volume of diluent to produce a second diluted fluid suspension of determinable concentration which is directed to another station.
The fluid sample is obtained by dipping an aspirator tube or snorkel into a sample contained in a suitable vessel and a quantity thereof is drawn into the transfer valve.
It must be understood that the entire apparatus is fluid filled and that transfers of fluid units are carried out hydraulically under selective applications of fluid pressure and vacuum in accord with a prearranged program.
As previously stated, an aspirator tube, snorkel or other thief apparatus generally operated in accordance with programmed alternating pressure-vacuum operations is utilized for sample pickup. In the course of such and further operations, sample blood remaining in the aspirator tube, line or valving is subjected to clearance only by the action of the greater volume of the next succeeding sample. Accordingly, some residual sample was mixed with the next sample. This is called "carry-over" and is an undesirable occurrence. If the samples were from the same patient source, perhaps deleterious results may not follow. Generally, the first few runs after change of sample are required to be discarded due to such carry-over from one sample to another. Notwithstanding the similarity of the succession of samples, differences in character and viscosity, for example, may prevent a succeeding sample from clearing the earlier sample from the aspirator tube, fluid line, valve, etc., thus mixing and contamination may be encountered.
Means for clearing the aspirator tube of residual fluid and yet capable of being controlled by the program of the system as a whole would be desirable but as yet, have not been available.